Remote Control School Bell

Example video

What you'll need:
- a wireless doorbell
- 1 x transistor (like bc547)
- 1 x relay
- 1 x 1K resistor

Tools:
- some solder
- a soldering iron
- ....

Step 1: How It Works

Normal:
When you push the button
=> The remote sends a signal.
=> The doorbell receives  the signal and makes a pin high in an IC on the PCB.
=> That pin TRIGGERS the sound controller.
=> The sound controller sends a signal to a speaker.
=> The speaker makes an annoying sound.

Hacked:
When you push the button: 
=> The remote sends a signal.
=> The doorbell receives the signal and makes a pin high in an IC on the PCB.
=> That pin TRIGGERS our new circuit.
(the transistor lets a current flow so the relay can switch on).
=> The relay switches on and lets a current flow trough the school bell.
=> The school bell rings "tringggg!!!!!!!!!!!! ".
=> And you can leave the class :D

Step 2: How to Find the Trigger Pin

Use the flowchart

Step 3: Making the Circuit

V+ is connected to the positive lead on the battery-pack of the doorbell.
GND is connected to the negative lead on the battery-pack of the doorbell.
Trigger is connected to the triggering pin of the doorbell.

G5-8 = are normal battery's 
R1 = 1KOhm
D1 = A normal diode like 1n4007 or 1n4004
K1 = NO relay 5V
T1 = A standard transistor like BC547 

Step 4: Testing

When the school bell is not connected you can hear the relay switching when you push the button.

TEST 1

And when everything is connected the bell will start ringing when you push the button till you lose the button.

TEST 2